The present invention relates to a control device for a machine that regulates fluid flow. More particularly, the control device produces a variable control signal between a preset maximum value and a minimum value, proportional to the distance between movable members to control a fluid-supplying machine.
The biomedical, chemical and food processing industries have numerous processes that require real-time fluid-flow control. These processes typically use automatic valves and variable pressure pumps controlled by a signal from a computer or human operator. In most applications using real-time control, the operator who controls the fluid-supplying machine needs accurate rate control and the ability to quickly respond to unexpected events. Satisfaction of these needs requires a control device that is located near the flow rate instrumentation and that produces either an analog control signal or a multi-bit digital control signal. The ideal control device for real-time control applications also provides an intuitive user interface that can reduce the possibility of error in an emergency situation.
The design of a mobile control device must also account for environmental concerns in addition to providing an appropriate control signal. This is a significant problem in the biomedical, chemical, and food processing industries because contaminants can ruin many of the associated products. Bacterial contamination is a particular problem for biomedical and processed food companies because their products usually require sterile conditions. These industries require constant sterilization of the control device without damaging or degrading the functional performances of the electrical and mechanical components. Furthermore, any control device used in these industries must be designed without openings that can trap contaminants between moving parts.
In addition to the contamination problem, many operations in the biomedical, chemical, and food processing industries involve the use of corrosive fluids. Control devices used in these applications must resist corrosion and must allow an operator to effectively clean all exposed surfaces. Because corrosive fluids can quickly damage electronics, a well-designed control device should also protect its electrical components.
One common control device design uses push-buttons to produce a binary control signal. However, this method will not work satisfactorily in many applications because the fluid can only flow at two predetermined rates. The addition of variable control would significantly improve this design because the fluid-supplying machine could then operate anywhere between a maximum and minimum flow rate. Adding this feature would allow a user to optimize operation of the fluid-supplying machine.
A common improvement to the push-button controller increases the number of operating states with a microprocessor. In this design, one button typically increases the fluid flow from one operating point to another. A second button decreases the flow rate, and a third button resets the machinery. An operator must press a button several times or hold down a button for several seconds to make a large change in fluid flow rate. Different implementations reduce the time necessary to move between flow rates by increasing the increment caused by each press of a button. However, this decision trades off speed of response against control accuracy. The push-button design also causes accidents because an operator can mistakenly press the wrong button in an emergency.
The controllers currently used in industry also have other flaws. For example, many of the controllers fail to seal their electronic components from the environment. This omission exposes the sensors to corrosion, increases the risk of shorting in the electrical system, and decreases the number of cleaning methods a customer can use on the control device.
The above-described control devices have all been created to control a fluid-supplying machine. However, none of these devices combines the advantages of a variable control signal with the ability to be cleaned and sterilized. These shortcomings greatly detract from the utility of existing control devices in the biomedical, chemical, and food processing industries. Therefore, a substantial need exists for a sealed control device able to provide a variable control signal to a fluid-supplying machine.